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Cat Scan

What Is Cat Scan?

CT scan is a non-invasive exam that combines the principles of x-ray with advanced computer technology to produce precise cross-sectional views of the internal organs and structures of the body. A 360 degree x-ray beam and computer production of images are used to create slices of the body and create a more three-dimensional picture than a traditional x-ray. CT scan is more comprehensive and detailed than conventional x-ray as it enables the body to be viewed slice by slice, from all angles rather than as a snapshot or photograph. A CT scan is used to define normal and abnormal structures in the body and/or assist in procedures by helping to accurately guide the placement of instruments and treatments. Since CT provides detailed information in a short period of time, it is often the imaging modality of choice in emergency situations.

Can I Have A Cat Scan? What Are The Risks?

The following may affect you being able to have a CT scan:

  • Known or possible pregnancy
  • Barium used for another test. These substances show up on a CT scan. If a CT scan of your belly is needed, it should be done before any tests that use barium.
  • You are not able to lie still during the exam.
  • Metal objects in the body, such as surgical slips or metal in joint replacements, may prevent a clear view of the area of interest.

A CT scan is a very safe study. Although CT exams require the use of ionizing radiation (x-ray) and there is a slight risk from x-ray radiation exposure, the amount of radiation used is minimized by advanced CT detectors and computer technology to achieve the best image quality at the lowest possible radiation dose. Also, protective shielding is used routinely to prevent unnecessary radiation exposure.

For CT examinations performed WITHOUT intravenous contrast, there is no risk involved in the exam unless you are or may be pregnant. The risks and benefits of having the CT scan should then be discussed with your doctor to determine the best course of action.

For CT examinations performed WITH intravenous iodinated contrast, most patients have no reaction or side effects. However, as with most diagnostically beneficial medical examinations, there are certain risks. The risks are related to allergic and non-allergic reactions to the injected contrast.

Minor reactions to the IV contrast used for CT scan may include nausea, vomiting, headache or dizziness, which are usually of short duration and usually require no treatment. Sometimes there are cases of hives (urticaria) and rash, which we can treat with antihistamines or other medications. Rarely, asthma can be induced, which is also treatable.

More serious reactions to the IV contrast used for CT scan, such as blood clotting, kidney damage, inflammation of a vein (phlebitis), shock and fatal reactions have occurred but only rarely. The incidence of fatal reaction is less than 1 in 100,000 patients receiving IV contrast with iodine, which is much less than reactions to many antibiotics and other medications used daily in medical practice.

If you would like more information or have any questions about the use of IV contrast, the CT staff and/or radiologist will speak with you at the time of your appointment. Also, please see the "if contrast is used section" for further information regarding the use of IV contrast.

If you are breastfeeding and receive IV contrast, you will need to use formula for 2 days after your CT scan so that you do not pass the dye to your baby. You should throw out any breast milk you collect during this time.

How Does It Work?

The CT scanner is a large doughnut-shaped machine. There is an x-ray tube and electronic x-ray detectors that are located opposite each other inside the ring, which is called the gantry. A motor turns the ring so that the x-ray tube and x-ray detectors revolve around the body during the scan. You will lie on a narrow, movable table that will slide you through the ring into the center of the CT machine. Once inside the scanner, numerous x-ray beams rotate around you at many different angles as the small detectors inside the scanner measure the amount of radiation that makes it through the part of the body being studied. The computer uses this information, along with advanced mathematical algorithms, to create several individual images called slices which can be stacked to create a three-dimensional image of the body. A computer workstation that processes the imaging information is located in the next room where the technologist operates the scanner and monitors the exam.

Preparation For Your Ct Scan

For all patients having a CT scan:

  • You may take all medications on your usual schedule as directed by your doctor.
  • Please bring a list of all of your current medications.

All CT scans with IV contrast:

  1. Your physician will order a lab test to check your creatinine level before the test. Since the kidneys filter out the IV contrast after the exam, it is important to have this lab test so that we know if your kidneys are working properly. This blood work must be done at least two days before the exam. If a creatinine result from a test that has been performed within one month of the appointment date is available, new lab work is not needed.
  2. Do no eat or drink anything for 4 hours prior to the exam.

CT scan of the abdomen/pelvis:

  1. Pick up drinks in the x-ray department at least one day prior to your appointment, along with the instructions on what time to drink the oral contrast.
  2. Do not eat or drink anything for 4 hours prior to the exam.
  3. If this exam has been ordered with IV contrast, please follow above instructions for required lab work.

Any other CT examination requires no additional preparation.

When To Arrive/what To Expect When You Do

You should arrive 10 minutes before your appointment time and report to the Radiology front desk area at the Landmark campus where you will be checked in. You will wait in the main Radiology waiting room where you will be greeted by a CT technologist who will bring you back to the CT scan area. The technologist will interview you to obtain medical history, as well as explain the exam and answer any questions that you may have prior to performing the exam. You may have to wear a gown depending on the area of the body being scanned.

What To Expect During The Cat Scan:

  • The technologist will position you on the table for best quality images. You will be lying on your back and may have to raise your arms above your head.
  • You will have to lie flat and very still for the entire exam as movement reduces the quality of the images.
  • You may be asked to hold your breath briefly as pictures are taken during the scan.
  • The technologist will watch you from the room next door and will communicate with you via intercom.
  • If you feel uncomfortable or need assistance at any point, the technologist is readily available to assist you.
  • If intravenous contrast is used, you will be injected. At the time of injection, you may have a brief feeling of warmth and flushing, a salty or metallic taste in your mouth or feel the urge to urinate. This feeling should not last. If you feel any other symptoms such as itching, headache, dizziness, difficulty breathing, nausea and/or vomiting please inform the technologist immediately.
  • Depending on the type of machine and the area(s) of interest, the exam may take up to 30 minutes.

If Intravenous Contrast Is Used

Contrast may sometime be needed to highlight your organs, blood vessels or tissues and to help make normal and abnormal structures more visible. Its use improves the radiologist's ability to make a detailed and correct diagnosis of disease processes or injury and/or to provide reassurance that nothing at all is wrong with the part of the body being examined.

The contrast that is used for CT exams is called Isovue. It contains iodine. Most patients will feel a warm sensation during or after the injection, but will have no reaction or side effects. However, there is a risk of reaction to the IV contrast. Please see the section entitled "Can I have a Cat scan? What are the risks?" for further information.

If your CT exam requires IV contrast, you will be screened by the technologist for the following conditions/diseases before any contrast is injected:

  • A previous adverse reaction to contrast media
  • A history of asthma or allergies
  • Allergy to any medications, iodine dye or foods (especially shellfish)
  • Heart condition/dysfunction
  • Pulmonary hypertension
  • Kidney disease
  • Diabetes and/or are taking Metformin (Glucophage)
  • Sickle cell disease
  • Pheochromocytoma
  • Multiple myeloma
  • Thyrotoxicosis

At the time of your appointment, the technologist will answer any questions you may have about the use of intravenous contrast prior to injection and you will be required to sign a consent form.


Our equipment is serviced regularly to ensure your safety, and our technologists are highly skilled and extremely knowledgeable. Also, our professional CT staff will interview you thoroughly prior to the exam and fill out a comprehensive history sheet relating to both your past medical history and your present symptoms. If there are any contraindications, the scan will not be performed. If your specific CT exam requires you to have IV contrast, the risks will be explained to you prior to the administration of any contrast and you must sign a consent form. In the event of a reaction to the IV contrast, our radiologists and staff will respond and treat the reaction immediately and monitor your symptoms closely.

What To Expect After The Cat Scan

There are no side effects, after-effects or restrictions after the exam. You may perform all regular activities and may take all medications, except Metformin (Glucophage) if you had a CT scan with IV contrast. Please see the next section "Special Instructions for Diabetic Patients on Metformin."

If you had a CT scan with IV contrast, you should drink extra fluids to help remove the contrast from your body.

Special Instructions For Diabetic Patients On Metformin

Metformin is a drug commonly used to treat diabetes and control blood sugar levels.
Metformin has a variety of brand names including the following:

  • Glucophage or Glucophage XR
  • Glucovance
  • Actoplus Met or Actoplus Met XR
  • Glumetza
  • Avandamet
  • Fortamet
  • Janumet
  • Metaglip
  • Riomet
  • Prandimet

In a few instances, the combination of Metformin and the IV contrast (x-ray dye) can cause a rare condition known as lactic acidosis. Please follow these special instructions to prevent this problem from occurring.

If you are on any of the above medications and you have had a CT scan with IV contrast, you will be informed by the CT staff to stop taking it immediately after your CT scan, and you should not take this medication for two days after the CT scan. Your doctor will also be notified of this. The radiologist will give you a prescription ordering another lab test to re-check your creatinine level (kidney function) before you can start taking Metformin again. You will need to call your doctor for the results of the blood test and to find out when to resume taking Metformin.

What About The Results

Our radiologists will read the exam within 24 hours. If your physician requests a STAT reading, it will be provided to them via phone call and/or fax immediately following your exam. The results will also be available via internet as soon as the final report is dictated by the radiologist. A copy of the final report will be forwarded to the ordering physician and/or primary care physician who will discuss the results with you.